Sorry for the delayed response and inconvenience caused. As per the description above, when you are converting a PDF file with Tables to Word document, the table borders are missing, Is that correct?
The record shows that you are subscribed to Adobe ExportPDF service with your current Adobe ID, try exporting the PDF file through the URL https://cloud.acrobat.com/exportpdf with your Adobe ID and password on a browser like Chrome, or Firefox, or Safari and see if this brings any difference.
is it possible to share the PDF file with us so that we can try it at our end? To share the file, please use Adobe Send feature, upload the file, share the link to files via private message only, How Do I Send Private Message